Media captionFootage shows people trying to escape from the building in Odessa

At least 31 people have been killed in a fire in an official building amid violence in Odessa in south-west Ukraine, the interior ministry says.

The deaths came as pro-Russian protesters clashed with Ukrainian government supporters in the city.

Officials said some people were overwhelmed by smoke and others died after they jumped from the building.

Earlier President Oleksandr Turchynov said many separatists had been killed in a government offensive in Sloviansk.

Activists have seized scores of government buildings and detained observers in eastern Ukraine.

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Reports suggest that both pro-Russians and supporters of Kiev were throwing petrol bombs in the area

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People were trapped on upper storeys of the building as the flames took hold

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Protesters were pictured throwing petrol bombs at the building

The fire broke out in Odessa's Trade Unions House, the regional office of Ukraine's interior ministry said. It did not give details of how the blaze started.

The exact sequence of events is still unclear, but reports suggest the separatists had barricaded themselves inside the building and both sides were throwing petrol bombs.

The interior ministry gave a toll of at least 31 dead, revising down an earlier tally of 38 killed.

Ukrainian Deputy Foreign Minister Danylo Lubkivsky told the BBC he regretted the loss of life but insisted Russia was behind the violence.

"The situation remains under control. But the security situation is threatened by Russian special agents," he said.

"That's why we are requesting and demanding Russian authorities to stop their efforts that can undermine regional security and stability."

Russia's foreign ministry said Moscow was "outraged" by events in Odessa and denounced Kiev's "irresponsibility".

The US called the violence "unacceptable" and urged both Ukraine and Russia to restore order.

"The violence and mayhem that led to so many senseless deaths and injuries is unacceptable," the state department said in a statement.

Gunfire

Earlier, four people were killed in clashes between the pro-Russian and pro-Kiev protesters in the city - the first such eruption of violence in the south after weeks of mounting unrest in Ukraine's east.

It followed a rally by Ukrainian football fans, reports say.

The BBC's David Stern in Kiev says the death toll in Odessa is the highest since violence broke out between pro-EU protesters and police in the capital in February.

The Black Sea city is ethnically mixed with a large number of Russian speakers, our correspondent says.

Meanwhile the latest reports from rebel-controlled Sloviansk in the east say intense gunfire has broken out in the centre of the city.